1. Field of the Invention
The present invention relates to an automatic toll charging system which communicates by radio between roadside units disposed at gates of a toll road and a vehicle-mounted unit mounted on a vehicle, and automatically charges a toll in a range from an entrance gate to an exit gate, and also relates to a vehicle-mounted unit used in an automatic toll charging system.
2. Description of Related Art
In recent years, a nonstop automatic toll charging system which automatically charges a toll from a vehicle without stopping has been proposed. This type of system is disclosed in JP-A-4-248693, in which a vehicle-mounted unit holds an IC card as an information recording medium, and at an entrance gate of a toll road (a toll gate at an entrance), the vehicle-mounted unit transmits roadside unit vehicle information (necessary information for verifying the vehicle) retrieved from the IC card. The roadside unit compares the vehicle information with other vehicle information detected by a vehicle type detection apparatus disposed on the roadside unit, and if the result of verification is favorable, the roadside unit transmits entrance information (a passing gate number, time information) to the vehicle-mounted unit in order to make the vehicle-mounted unit record them in the IC card.
The roadside unit verifies the vehicle information by means of the above method at an exit gate of the toll road (a toll gate at an exit). If the result of verification is favorable, the vehicle-mounted unit transmits the entrance information recorded in the IC card to the roadside unit. The roadside unit calculates the toll, and then transmits the toll and the time information to the IC card and a central unit in order to record them as past recorded information in the IC card and the central unit.
As mentioned above, with regard to a two piece type unit in which the IC card can be separated from the vehicle-mounted unit, a toll payment process is completed with information exchanged between the IC card and the roadside unit. In this case, it is necessary to consider two information exchanging steps, where one is executed between the IC card and the vehicle-mounted unit, and the other is executed between the vehicle-mounted unit and the roadside unit, when the information exchanging is executed.
When the nonstop automatic toll charging system is used in practice, it is necessary to transmit the information rapidly so as to ensure the exchange of the information by means of radio communication between the roadside unit and the vehicle. On the one hand, in radio communication between the vehicle-mounted unit and the roadside unit, it is possible to transmit the information with sufficient information transmission speed; on the other hand, between the IC card and the vehicle-mounted unit, it is difficult to transmit the information rapidly because of the limitations of the capabilities of the IC card.
Therefore, as disclosed in JP-A-4-248693, problems due to the difficulties of transmitting the information rapidly arises if the vehicle information and the entrance information are transmitted to the roadside unit from the IC card. Thus, it could be proposed that the information exchanged between the road and the vehicle is basically executed between the vehicle-mounted unit and the roadside unit, and information exchange between the IC card and the vehicle-mounted unit is executed before or after the information exchange between the roadside unit and the vehicle.
In this case, it is important to consider how the entrance information for the toll payment is managed. A method of management by means of a host computer in a central unit or a method of management by means of the vehicle-mounted unit could be proposed. However, the former method is not realistic because it requires a real-time inquiry for the host computer at the exit gate, and loads an information communication network used by the system and the host computer. If the entrance information is held and managed in the vehicle-mounted unit, the later method is realistic because it is possible to execute the calculation and toll payment based on the entrance information at the exit gate. However, if the later method is adopted, when a function of the vehicle-mounted unit goes wrong (it is especially likely that a communication function between the roadside unit and the vehicle-mounted unit may go wrong), it becomes difficult to calculate the toll at the exit gate.
Furthermore, it could be proposed that the IC card be utilized for various purposes in addition to the automatic toll charging system because many functions may be performed by the IC card. In this case, another IC card may be used after passing through the entrance gate because the IC card is not exclusively used by the automatic toll charging system. For instance, another IC card may be used when the IC card is pulled out from the vehicle-mounted unit and used for the payment of a meal at a service area, or when another IC card is used because the original IC card is lost, or when the toll payment is executed by means of a passenger's IC card.
Therefore, with utility of the IC card under consideration, it is convenient that another IC card can be used for the toll payment like the original IC card which is used until the time when the original IC card is exchanged for another IC card even if the original IC card is exchanged for another IC card after passing through the entrance gate.